DOCSLIB.ORG

High Power Mode-Locked Semiconductor Lasers and Their Applications

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

University of Central Florida STARS Electronic Theses and Dissertations, 2004-2019 2008 High Power Mode-locked Semiconductor Lasers And Their Applications Shinwook Lee University of Central Florida Part of the Electromagnetics and Photonics Commons, and the Optics Commons Find similar works at: https://stars.library.ucf.edu/etd University of Central Florida Libraries http://library.ucf.edu This Doctoral Dissertation (Open Access) is brought to you for free and open access by STARS. It has been accepted for inclusion in Electronic Theses and Dissertations, 2004-2019 by an authorized administrator of STARS. For more information, please contact [email protected]. STARS Citation Lee, Shinwook, "High Power Mode-locked Semiconductor Lasers And Their Applications" (2008). Electronic Theses and Dissertations, 2004-2019. 3722. https://stars.library.ucf.edu/etd/3722 HIGH POWER MODE-LOCKED SEMICONDUCTOR LASERS AND THEIR APPLICATIONS by SHINWOOK LEE B.Sc. Sogang University, Republic of Korea, 1993 M.Sc. Sogang University, Republic of Korea, 1995 A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the College of Optics and Photonics/CREOL at the University of Central Florida Orlando, Florida Spring Term 2008 Major Professor: Peter J. Delfyett, Jr. © 2008 Shinwook Lee ii For My Mother and Wife. iii ABSTRACT In this dissertation, a novel semiconductor mode-locked oscillator which is an extension of eXtreme Chirped Pulse Amplification (XCPA) is investigated. An eXtreme Chirped Pulse Oscillator (XCPO) implemented with a Theta cavity also based on a semiconductor gain is presented for generating more than 30ns frequency-swept pulses with more than 100pJ of pulse energy and 3.6ps compressed pulses directly from the oscillator. The XCPO shows the two distinct characteristics which are the scalability of the output energy and the mode-locked spectrum with respect to repetition rate. The laser cavity design allows for low repetition rate operation <100MHz. The cavity significantly reduces nonlinear carrier dynamics, integrated self phase modulation (SPM), and fast gain recovery in a Semiconductor optical Amplifier (SOA). Secondly, a functional device, called a Grating Coupled Surface Emitting Laser (GCSEL) is investigated. For the first time, passive and hybrid mode-locking of a GCSEL is achieved by using saturable absorption in the passive section of GCSEL. To verify the present limitation of the GCSEL for passive and hybrid mode-locking, a dispersion matched cavity is explored. In addition, a Grating Coupled surface emitting Semiconductor Optical Amplifier (GCSOA) is also investigated to achieve high energy pulse. An energy extraction experiment for GCSOA using stretched pulses generated from the colliding pulse semiconductor mode-locked laser via a chirped fiber bragg grating, which exploits the XCPA advantages is also demonstrated. Finally, passive optical cavity amplification using an enhancement cavity is presented. In order to achieve the interferometric stability, the Hänsch-Couillaud Method is employed to stabilize the passive optical cavity. The astigmatism-free optical cavity employing an acousto- iv optic modulator (AOM) is designed and demonstrated. In the passive optical cavity, a 7.2 of amplification factor is achieved with a 50 KHz dumping rate. v ACKNOWLEDGMENTS First of all, I would like to thank to my adviser, Prof. Delfyett, who has introduced the world of ultrafast optics. Personally and scientifically, I have learned a lot of things from him. His positive attitude and strong enthusiasm for life is also what I would like to earn during my Ph.D course. I have enjoyed a supportive atmosphere of the ultrafast group in CREOL. It was fortunate for me to have such supportive and good colleagues. They are Prof. Sangyun Gee, Dr. Michael Mielke, Dr. Tolga Yilmaz, Dr. Myoung Taek Choi, Dr. Kyungbum Kim, Dr. Wangkuen Lee, Dr. Luis Archundia, Dr. Bojan Resan, Dr. Nishant Bhatambrekar, Franklyn Quinlan, Sarper Ozharar, Ji- Myoung Kim, Mr. Dimitrios Mandridis, Ibrahim Ozdur, Mohammad Umar Piracha, Charles Williams, Iffat Nayyar, Sharad Bhooplapur, Abhijeet Ardey, Henock Legesse, Dat Nguyen, Nazanin Hoghooghi, Josue Davila-Rodriguez, Sen-Yong Chen and my lab mate, Dimitrios Mandridis. I express my sincere thanks to all of professors in CREOL and staffs for establishment of such a solid structure of photonics research. Especially, I also want to acknowledge my committee members for this dissertation, who are Prof. Likamwa, Prof. Riza, and Prof. Kapoor. Finally, I dedicate this dissertation to my wife, Kyunglae Kang, and my mother, Chiae Kim. Without their prayer and love, this dissertation could not have been done. vi TABLE OF CONTENTS ABSTRACT................................................................................................................................... iv ACKNOWLEDGMENTS ............................................................................................................. vi TABLE OF CONTENTS.............................................................................................................. vii LIST OF FIGURES ....................................................................................................................... xi LIST OF TABLES.....................................................................................................................xviii LIST OF ACRONYMS/ABBREVIATIONS.............................................................................. xix CHAPTER 1 INTRODUCTION .................................................................................................... 1 1.1 Semiconductor gain media .................................................................................................... 1 1.1.1 Semiconductor laser........................................................................................................ 1 1.1.2 Semiconductor optical amplifiers ................................................................................... 4 1.2 Carrier dynamics of semiconductor gain media.................................................................... 7 1.3 Semiconductor mode-locked lasers..................................................................................... 11 1.3.1 Active mode-locking..................................................................................................... 13 1.3.2 Passive and hybrid mode-locking ................................................................................. 14 1.4 Scope and organization of the dissertation.......................................................................... 17 CHAPTER 2 EXTREME CHIRPED PULSE AMPLIFICATION.............................................. 20 2.1 High power semiconductor mode-locked laser ................................................................... 20 2.2 Concept of extreme chirped pulse amplification................................................................. 21 2.3 Colliding pulse semiconductor mode-locked laser.............................................................. 23 2.4 Chirped fiber bragg grating for XCPA................................................................................ 32 2.5 Extreme chirped pulse amplification system....................................................................... 34 vii 2.6 Summary.............................................................................................................................. 37 CHAPTER 3 EXTREME CHIRPED PULSE OSCILLATOR BASED ON THETA CAVITY DESIGN.................................................................................................................................. 39 3.1 A more of extreme chirped pulse amplification .................................................................. 39 3.2 Preliminary experiment for extreme chirped pulse oscillator ............................................. 41 3.3 Theta cavity design for extreme chirped pulse oscillator.................................................... 45 3.4 Extreme chirped pulse oscillator for > 1ns stretched pulses ............................................... 55 3.4.1 Theta cavity and experimental setup............................................................................. 56 3.4.2 Experimental results...................................................................................................... 62 3.5 Amplification of stretched pulses from the XCPO.............................................................. 69 3.6 <100MHz repetition rate operation of the Theta cavity ...................................................... 74 3.7 Preliminary experiment of feed forward intensity noise cancellation and gain flattening scheme for frequency swept pulses ..................................................................................... 78 3.8 Summary.............................................................................................................................. 80 CHAPTER 4 GRATING COUPLED SURFACE EMITTING LASER AND GRATING COUPLED SURFACE EMITTING SEMICONDUCTOR OPTICAL AMPLIFIER ........... 82 4.1 Introduction ......................................................................................................................... 82 4.2 Grating coupled surface emitting laser................................................................................ 85 4.3 Passive and hybrid mode-locking of grating coupled surface emitting laser...................... 89 4.3.1 Experimental setup for mode-locking..........................................................................
Recommended publications
  • Semiconductor Light Sources

    Semiconductor Light Sources

    Laser Systems and Applications Couse 2020-2021 Semiconductor light sources Prof. Cristina Masoller Universitat Politècnica de Catalunya [email protected] www.fisica.edu.uy/~cris SCHEDULE OF THE COURSE Small lasers, biomedical Semiconductor light sources lasers and applications . 1 (11/12/2020) Introduction. 7 (19/1/2021) Small lasers. Light-matter interactions. 8 (22/1/2021) Biomedical lasers. 2 (15/12/2020) LEDs and semiconductor optical amplifiers. Laser models . 3 (18/12/2020) Diode lasers. 9 (26/1/2021) Laser turn-on and modulation response. Laser Material Processing . 10 (29/1/2021) Optical injection, . 4 (22/12/2020) High power laser optical feedback, polarization. sources and performance improving novel trends . 11 (2/2/2021) Students’ . 5 (12/1/2021) Laser-based presentations. material macro processing. 12 (5/2/2021) Students’ . 6 (15/1/2020) Laser-based presentations. material micro processing. 9/2/2021: Exam Lecturers: C. Masoller, M. Botey 2 Learning objectives . Understand the physics of semiconductor materials and the electron-hole recombination mechanisms that lead to the emission of light. Learn about the operation principles of light emitting diodes (LEDs) and semiconductor optical amplifiers (SOAs). Become familiar with the operation principles and characteristics of laser diodes (LDs). 3 Outline: Semiconductor light sources . Introduction . Light-matter interactions in semiconductor materials . Light Emitting Diodes (LEDs) . Semiconductor optical amplifiers (SOAs) . Laser diodes (LDs) The start of the laser diode story: the invention of the transistor Nobel Prize in Physics 1956 “For their research on semiconductors and their discovery of the transistor effect”. The invention of the transistor in 1947 lead to the development of the semiconductor industry (microchips, computers and LEDs –initially only green, yellow and red).
  • Temporal and Spectral Characterization of Near-Ir Femtosecond Optical Parametric Oscillator Pulses

    Temporal and Spectral Characterization of Near-Ir Femtosecond Optical Parametric Oscillator Pulses

    MSc in Photonics PHOTONICSBCN Universitat Politècnica de Catalunya (UPC) Universitat Autònoma de Barcelona (UAB) Universitat de Barcelona (UB) Institut de Ciències Fotòniques (ICFO) http://www.photonicsbcn.eu Master in Photonics MASTER THESIS WORK TEMPORAL AND SPECTRAL CHARACTERIZATION OF NEAR-IR FEMTOSECOND OPTICAL PARAMETRIC OSCILLATOR PULSES Parisa Farzam Supervised by Dr. Majid Ebrahim-Zadeh, (ICFO, ICREA) and Dr. Lukasz Kornaszewski (ICFO) Presented on date 9th September 2009 Registered at Temporal and spectral characterization of near-IR femtosecond optical parametric oscillator pulses Parisa Farzam ICFO-Institut de Ciències Fotòniques, Nonlinear optics group, Mediterranean Technology Park, 08860 Castelldefels (Barcelona), Spain E-mail: [email protected] Abstract. Recently, there has been growing interest in ultrashort pulse measurement techniques. The aim of this work is to utilize interferometric autocorrelator in order to characterize near- IR femtosecond optical parametric oscillator (OPO) pulses. Although considerable research has been devoted to using nonlinear crystals in the autocorrelators, an attractive alternative to this approach remains two-photon absorption in photodiodes. In the setup we have used a commercial semiconductor which has several advantages to second harmonic generation technique. Conventional methods in autocorrelation analysis use secant hyperbolic square (sech2) assumption to figure out the shape of pulse; but we have developed a software to find out the pulse shape by guessing the phase. The comparison between results from phase-guessing method and sech2 assumption shows that the first method is more flexible and gives much information but it needs to be enhanced in order to find the best phase automatically. Keywords: ultrashort pulse measurement, autocorrelation, two-photon absorption, optical parametric oscillator.
  • White Paper Introduction to Optical Amplifiers

    White Paper Introduction to Optical Amplifiers

    White Paper Introduction to Optical Amplifiers June 2010 1 Introduction Optical amplifiers are a key enabling technology for optical communication networks. Together with wavelength-division multiplexing (WDM) technology, which allows the transmission of multiple channels over the same fiber, optical amplifiers have made it possible to transmit many terabits of data over distances from a few hundred kilometers and up to transoceanic distances, providing the data capacity required for current and future communication networks. The purpose of this paper is to provide an overview of optical amplifiers. For a more detailed discussion on the implementation of optical amplifiers using Erbium doped fiber amplifier (EDFA) technology see Finisar’s white paper “Introduction to EDFA technology”. 2 What Are Optical Amplifiers? A basic optical communication link comprises a transmitter and receiver, with an optical fiber cable connecting them. Although signals propagating in optical fiber suffer far less attenuation than in other mediums, such as copper, there is still a limit of about 100 km on the distance the signals can travel before becoming too noisy to be detected. Before the commercialization of optical amplifiers, it was necessary to electronically regenerate the optical signals every 80-100 km in order to achieve transmission over long distances. This meant receiving the optical signal, cleaning and amplifying it electronically, and then retransmitting it over the next segment of the communication link. While this can be feasible when transmitting a single low capacity optical channel, it quickly becomes unfeasible when transmitting tens of high capacity WDM channels, resulting in a highly expensive, power- hungry and bulky regenerator station, as shown in Figure 1a.
  • Optical Amplifiers.Pdf

    Optical Amplifiers.Pdf

    ECE 6323 . Introduction . Fundamental of optical amplifiers . Types of optical amplifiers Erbium-doped fiber amplifiers Semiconductor optical amplifier Others: stimulated Raman, optical parametric . Advanced application: wavelength conversion . Advanced application: optical regeneration . What is optical amplification? . What use is optical amplification? Review: stimulated emission • Through a population, net gain occurs when there are more stimulated photons than photons absorbed • Require population inversion from input pump • Amplified output light is coherent with input light Optical amplification Energy pump Pin Pout Pin P Coherent z P Pin (N2 N1) z dP gP dz Optically amplified signal: coherent with input: temporally, If g>0: Optical gain spatially, and with polarization (else, loss) . What is optical amplification? . What use is optical amplification? • The most obvious: to strengthen a weakened signal (compensate for loss through fibers) • …But why not just detect the signal electronically and regenerate the signal? • System advantage: boosting signals of many wavelengths: key to DWDM technology • System advantage: signal boosting through many stages without the trouble of re-timing the signal • There are intrinsic advantages with OA based on noise considerations • Can even be used for pre-amplification of the signal before detected electronically . Introduction . Fundamental of optical amplifiers . Types of optical amplifiers Erbium-doped fiber amplifiers Semiconductor optical amplifier Others: stimulated Raman, optical
  • Second Harmonic Generation Microscopy for Quantitative Analysis

    Second Harmonic Generation Microscopy for Quantitative Analysis

    PROTOCOL Second harmonic generation microscopy for quantitative analysis of collagen fibrillar structure Xiyi Chen1, Oleg Nadiarynkh1,2, Sergey Plotnikov1,2 & Paul J Campagnola1 1Department of Biomedica l Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA. 2Present addresses: Department of Physics, University of Utrecht, Utrecht, The Netherlands (O.N.); US National Institutes of Health, Heart, Lung and Blood Institute, Bethesda, Maryland, USA (S.P.). Correspondence should be addressed to P.J.C. ([email protected]). Published online 8 March 2012; doi:10.1038/nprot.2012.009 Second-harmonic generation (SHG) microscopy has emerged as a powerful modality for imaging fibrillar collagen in a diverse range of tissues. Because of its underlying physical origin, it is highly sensitive to the collagen fibril/fiber structure, and, importantly, to changes that occur in diseases such as cancer, fibrosis and connective tissue disorders. We discuss how SHG can be used to obtain more structural information on the assembly of collagen in tissues than is possible by other microscopy techniques. We first provide an overview of the state of the art and the physical background of SHG microscopy, and then describe the optical modifications that need to be made to a laser-scanning microscope to enable the measurements. Crucial aspects for biomedical applications are the capabilities and limitations of the different experimental configurations. We estimate that the setup and calibration of the SHG instrument from its component parts will require 2–4 weeks, depending on the level of the user′s experience. INTRODUCTION Over the past decade, the nonlinear optical method of SHG micros­ on the harmonophores and their assembly that can be imaged, as copy has emerged as a powerful tool for visualizing the supra­ the environment must be noncentrosymmetric on the size scale molecular assembly of collagen in tissues at an unprecedented level of of λSHG; otherwise, the signal will vanish.
  • Lecture 9 and 10: Pulsed Lasers and Mode-Locking

    Lecture 9 and 10: Pulsed Lasers and Mode-Locking

    Lecture 9 and 10: Pulsed lasers and mode-locking 1. Ultrashort pulses Ultrashort pulse shorter than 1 ps (10-12 s) Shortest pulses generated from lasers: Type of laser Pulse duration Fiber laser ~35 - 50 fs Solid-state laser (e.g. Yb) ~40-50 fs Ti:Sapphire laser ~ 3 fs – 7 fs The shortest possible pulse of a given wavelength is one light cycle long: 1550 nm 4.3 fs 800 nm 2.7 fs Shorter wavelength shorter pulses 2. Measurement of ultrashort pulses Techniques: • Optical autocorrelation • FROG (Frequency Resolved Optical Gating) Improved version: GRENOULLIE • SPIDER (Spectral Phase Interferometry for Direct Electric-field Reconstruction) Autocorrelator Interferometric autocorrelation trace: FROG Source: Rick Trebino, Frequency Resolved Optical Gating SPIDER 3. Mode-locked lasers a) Difference between a CW and mode-locked laser: A mode-locked laser: Emits a train of equally-spaced, ultrashort pulses (femtosecond) - down to almost single- cycle Output spectrum is broad (tens-hundreds of nanometers)/ Broader spectrum shorter pulses In the frequency domain, the output consists of thousands/millions of narrow lines (comb- like structure) b) Relation between the number of synchronized modes and the pulse duration: More synchronized modes shorter pulse. c) Passive mode-locking and saturable absorber In order to achieve passive mode-locking we need a device called saturable absorber. The saturable absorber: - Blocks any CW radiation in the cavity - It forces the laser to synchronize the modes and generate pulses - Only high-intensity pulse
  • Nanoscale Force Sensing of an Ultrafast Nonlinear Optical Response

    Nanoscale Force Sensing of an Ultrafast Nonlinear Optical Response

    Nanoscale force sensing of an ultrafast nonlinear optical response Zeno Schumachera,1,2 , Rasa Rejalia, Raphael Pachlatkoa , Andreas Spielhofera, Philipp Naglerb, Yoichi Miyaharaa, David G. Cookea , and Peter Grutter¨ a,1 aDepartment of Physics, McGill University, Montreal QC H3A 2T8, Canada; and bDepartment of Physics, University of Regensburg, 93053 Regensburg, Germany Edited by Jianming Cao, Florida State University, Tallahassee, FL, and accepted by Editorial Board Member Zachary Fisk July 2, 2020 (received for review March 2, 2020) The nonlinear optical response of a material is a sensitive probe Results of electronic and structural dynamics under strong light fields. We split the output of a mode-locked femtosecond fiber laser The induced microscopic polarizations are usually detected via operating at 80-MHz repetition rate and 780-nm central wave- their far-field light emission, thus limiting spatial resolution. Sev- length, 200 mW (Toptica FemtoFiber pro NIR), to generate eral powerful near-field techniques circumvent this limitation two coherent pulse trains, with a well-defined temporal delay by employing local nanoscale scatterers; however, their signal between the two. The pulse trains can be arranged in a non- strength scales unfavorably as the probe volume decreases. Here, collinear or collinear fashion and focused onto the tip–sample we demonstrate that time-resolved atomic force microscopy is junction of an AFM incorporated in a UHV system. As the two capable of temporally and spatially resolving the microscopic, pulses are delayed with respect to each other, the light inten- electrostatic forces arising from a nonlinear optical polarization sity at the tip–sample junction oscillates, in delay time, with the in an insulating dielectric driven by femtosecond optical fields.
  • Section 5: Optical Amplifiers

    Section 5: Optical Amplifiers

    SECTION 5: OPTICAL AMPLIFIERS 1 OPTICAL AMPLIFIERS S In order to transmit signals over long distances (>100 km) it is necessary to compensate for attenuation losses within the fiber. S Initially this was accomplished with an optoelectronic module consisting of an optical receiver, a regeneration and equalization system, and an optical transmitter to send the data. S Although functional this arrangement is limited by the optical to electrical and electrical to optical conversions. Fiber Fiber OE OE Rx Tx Electronic Amp Optical Equalization Signal Optical Regeneration Out Signal In S Several types of optical amplifiers have since been demonstrated to replace the OE – electronic regeneration systems. S These systems eliminate the need for E-O and O-E conversions. S This is one of the main reasons for the success of today’s optical communications systems. 2 OPTICAL AMPLIFIERS The general form of an optical amplifier: PUMP Power Amplified Weak Fiber Signal Signal Fiber Optical AMP Medium Optical Signal Optical Out Signal In Some types of OAs that have been demonstrated include: S Semiconductor optical amplifiers (SOAs) S Fiber Raman and Brillouin amplifiers S Rare earth doped fiber amplifiers (erbium – EDFA 1500 nm, praseodymium – PDFA 1300 nm) The most practical optical amplifiers to date include the SOA and EDFA types. New pumping methods and materials are also improving the performance of Raman amplifiers. 3 Characteristics of SOA types: S Polarization dependent – require polarization maintaining fiber S Relatively high gain ~20 dB S Output saturation power 5-10 dBm S Large BW S Can operate at 800, 1300, and 1500 nm wavelength regions.
  • Practical Tips for Two-Photon Microscopy

    Practical Tips for Two-Photon Microscopy

    Appendix 1 Practical Tips for Two-Photon Microscopy Mark B. Cannell, Angus McMorland, and Christian Soeller INTRODUCTION blue and green diode lasers. To provide an alignment beam to which the external laser can be aligned, light from this reference As is clear from a number of the chapters in this volume, 2-photon laser needs to be bounced back through the microscope optical microscopy offers many advantages, especially for living-cell train and out through the external coupling port: studies of thick specimens such as brain slices and embryos. CAUTION: Before you switch on the reference laser in this However, these advantages must be balanced against the fact that configuration make sure that all PMTs are protected and/or commercial multiphoton instrumentation is much more costly than turned off. the equipment used for confocal or widefield/deconvolution. Given Place a front-surface mirror on the stage of the microscope and these two facts, it is not surprising that, to an extent much greater focus onto the reflective surface using an air objective for conve- than is true of confocal, many researchers have decided to add a nience (at sharp focus, you should be able to see scratches or other femtosecond (fs) pulsed near-IR laser to a scanner and a micro- mirror defects through the eyepieces). The idea of this method is scope to make their own system (Soeller and Cannell, 1996; Tsai to cause the reference laser beam to bounce back through the et al., 2002; Potter, 2005). Even those who purchase a commercial optical train and emerge from the other laser port.
  • State-Of-The-Art Fiber Optics for Short Distance Frequency Reference Distribution

    State-Of-The-Art Fiber Optics for Short Distance Frequency Reference Distribution

    N89-27878 January-March 1989 TDA Progress Report 42-97 State-of-the-Art Fiber Optics for Short Distance Frequency Reference Distribution G. Lutes and L. Primas Communications Systems Research Section A number of recently developed fiber-optic components that hem the promise of unprecedented stability for passively stabilized frequency distribution links are character- ized. These components include a fiber-optic transmitter, an optical isolator, and a new type of fiber-optic cable. A novel laser transmitter exhibits extremely low sensitivity to intensity and polarization changes of reflected light due to cable flexure. This virtually eliminates one of the shortcomings in previous laser transmitters. A high-isolation, low- loss optical isolator has been developed which also virtually eliminates laser sensitivity to changes in intensity and polarization of reflected light. A newly developed fiber has been tested. This fiber has a thermal coefficient of delay of less than 0.5 parts per million per °C, nearly 20 times lower than the best coaxial hardline cable and 10 times lower than any previous fiber-optic cable. These components are highly suitable for distribution systems with short extent, such as within a Deep Space Communications Complex. In this article these new components are described and the test results presented. I. Introduction mary causes of degradation. These effects are caused by distri- bution system noise, which reduces the SNR, and variations in The transmitter exciter, local oscillator, and receiver delay the environmental temperature, which cause delay changes. calibration system in a Deep Space Station (DSS) require The degree of delay change is dependent on the Thermal Coef- stable frequency references.
  • A Polarization-Insensitive Recirculating Delayed Self-Heterodyne Method for Sub-Kilohertz Laser Linewidth Measurement

    A Polarization-Insensitive Recirculating Delayed Self-Heterodyne Method for Sub-Kilohertz Laser Linewidth Measurement

    hv photonics Communication A Polarization-Insensitive Recirculating Delayed Self-Heterodyne Method for Sub-Kilohertz Laser Linewidth Measurement Jing Gao 1,2,3 , Dongdong Jiao 1,3, Xue Deng 1,3, Jie Liu 1,3, Linbo Zhang 1,2,3 , Qi Zang 1,2,3, Xiang Zhang 1,2,3, Tao Liu 1,3,* and Shougang Zhang 1,3 1 National Time Service Center, Chinese Academy of Sciences, Xi’an 710600, China; [email protected] (J.G.); [email protected] (D.J.); [email protected] (X.D.); [email protected] (J.L.); [email protected] (L.Z.); [email protected] (Q.Z.); [email protected] (X.Z.); [email protected] (S.Z.) 2 University of Chinese Academy of Sciences, Beijing 100039, China 3 Key Laboratory of Time and Frequency Standards, Chinese Academy of Sciences, Xi’an 710600, China * Correspondence: [email protected]; Tel.: +86-29-8389-0519 Abstract: A polarization-insensitive recirculating delayed self-heterodyne method (PI-RDSHM) is proposed and demonstrated for the precise measurement of sub-kilohertz laser linewidths. By a unique combination of Faraday rotator mirrors (FRMs) in an interferometer, the polarization-induced fading is effectively reduced without any active polarization control. This passive polarization- insensitive operation is theoretically analyzed and experimentally verified. Benefited from the recirculating mechanism, a series of stable beat spectra with different delay times can be measured simultaneously without changing the length of delay fiber. Based on Voigt profile fitting of high- order beat spectra, the average Lorentzian linewidth of the laser is obtained. The PI-RDSHM has advantages of polarization insensitivity, high resolution, and less statistical error, providing an Citation: Gao, J.; Jiao, D.; Deng, X.; effective tool for accurate measurement of sub-kilohertz laser linewidth.
  • Saturated Absorption Spectroscopy

    Saturated Absorption Spectroscopy

    Ph 76 ADVANCED PHYSICS LABORATORY —ATOMICANDOPTICALPHYSICS— Saturated Absorption Spectroscopy I. BACKGROUND One of the most important scientificapplicationsoflasersisintheareaofprecisionatomicandmolecular spectroscopy. Spectroscopy is used not only to better understand the structure of atoms and molecules, but also to define standards in metrology. For example, the second is defined from atomic clocks using the 9192631770 Hz (exact, by definition) hyperfine transition frequency in atomic cesium, and the meter is (indirectly) defined from the wavelength of lasers locked to atomic reference lines. Furthermore, precision spectroscopy of atomic hydrogen and positronium is currently being pursued as a means of more accurately testing quantum electrodynamics (QED), which so far is in agreement with fundamental measurements to ahighlevelofprecision(theoryandexperimentagreetobetterthanapartin108). An excellent article describing precision spectroscopy of atomic hydrogen, the simplest atom, is attached (Hänsch et al.1979). Although it is a bit old, the article contains many ideas and techniques in precision spectroscopy that continue to be used and refined to this day. Figure 1. The basic saturated absorption spectroscopy set-up. Qualitative Picture of Saturated Absorption Spectroscopy — 2-Level Atoms. Saturated absorp- tion spectroscopy is one simple and frequently-used technique for measuring narrow-line atomic spectral features, limited only by the natural linewidth Γ of the transition (for the rubidium D lines Γ 6 MHz), ≈ from an atomic vapor with large Doppler broadening of ∆νDopp 1 GHz. To see how saturated absorp- ∼ tion spectroscopy works, consider the experimental set-up shown in Figure 1. Two lasers are sent through an atomic vapor cell from opposite directions; one, the “probe” beam, is very weak, while the other, the “pump” beam, is strong.